Experimental work will be with the European corn borer, Ostrinia nubilalis, and designed to determine the role of photoperiod in the termination of larval diapause. Emphasis will be on the elucidation of the characteristics of the diapause state in terms of its apparent intensity and the relationship of intensity and diapause development to the photoperiods. The Dual System Theory of the biological clock will be subjected to further testing. The theoretical characteristics that are subject to artificial and natural selection toward ecological adaptation of insect populations will be investigated. Experiments will also be run on the applicability of the theory to the phenomenon of photoperiodic termination of the diapause state. BIBLIOGRAPHIC REFERENCES: Houk, E.J. and S.D. Beck (1975). Comparative ultrastructure and the brain of diapause and nondiapause larvae of the European corn borer, Ostrinia nubilalis Cell. Tiss. Res. 162: 499-510. Beck, S.D. (1975). Photoperiodic determination of insect development and diapause. III. Effects of nondiel photoperiods. J. Comp. Physiol. 103: 227-245.